In large piggeries, swine breeding is conducted in three stages, each taking place in a separate area. 1) piglets are first in the pig breeding shed where they stay with their mothers for about 14 days after their birth; 2) the piglets are then transferred to pig nursery pen; and 3) they are then transferred to the feeder barn for the last phase of breeding before slaughter. These three stages each require specific feed and produce specific manure. A pig produces an average of 7.6 L of manure per day which amounts in Canada only to about 30 millions m3 produced annually. Many problems are associated with manure production. A fraction of the manure produced may be used in land spreading for agricultural purposes but the soil's phosphorus saturation level is quickly reached and the surplus then trickles to surrounding surface waterways and underground water reserves. Air pollution results from odors produced by anaerobic fermentation in manure pits. Manure have average contents of 19.8 g/L BOD5, 52.4 g/L COD, 6.1 g/L total nitrogen and 1.9 g/L total phosphorus (Pt) (MAPAQ, 1986). The manure may also contain heavy metals such as copper and zinc that are present in the pig feed which therefore also end-up in the environment. Various methods have been devised for manure disposal or transformation.
In the province of Quebec, Canada, land spreading constitutes the technique most widely used for manure disposal. Most other known techniques may be classified in one of the following categories: 1) mechanical separation; 2) aerobic treatment (with or without nitrification and denitrification); 3) anaerobic treatment: 4) composting; 5) filtration, osmosis and ultrafiltration processes; 6) drying and fertilizers production; 7) biological treatment; and 8) flotation processes.
Mechanical Separation
Grisé (2000) describes in U.S. Pat. No. 6,033,570 a method comprising using a screw press to separate the solids of the manure after an addition of cellulose (vegetal) based product, followed by a treatment of the yielded liquid on biological filters. SLS Technologies uses a method based on centrifugation (FPPQ, 2001). Miknevich and Hassick, 1998 describe in U.S. Pat. No. 5,776,350 a method comprising, after an addition of polyacrilamides, filtering the manure in a mechanical separator having screens. The Solution Biofertile™ process uses a screen and a screw press as a first step of a more complex process comprising further treating the liquid so produced (FPPQ, 2001).
Aerobic Treatment with or without Nitrification and Denitrification
Marr (1968) describes a mesophilic aerobic treatment of the liquid fraction of the manure wherein temperatures of 7 to 37° C. are easily maintained by the microbiological activity. A further sanitization with composting or limestone treatment may be required since operating temperatures may not always be sufficiently high to eliminate pathogens (Degrémont, 1989; EPA, 1979).
Vallée et al., (1989) describes a method performed in St-Elzéar in the province of Québec comprising a first step of screening the solid fraction, followed by an anaerobic treatment of the liquid fraction in bioreactors, and a final polishing of the liquid fraction in aeration lagoons. The resulting water is used for irrigation of plots cultivated in forage corn. The recovered solid fraction amounts to about 25% of the raw manure and reduced the COD by 61%, the total solids by 83% and the total phosphorus (Pt) by 87%. The mesophilic aerobic treatment of the liquid in bioreactors required a minimum hydraulic retention time (HRT) of ten days achieving thereby a decrease of 84% of the COD, of 64% of the NH4, and of 56% of the Pt as compared to that existing In the bioreactor feed. The final lagooning is particularly efficient for the reduction of COD5 and the reduction of suspended solids (SS) which are of 97% and 88%, respectively, as compared to the concentration in the bioreactor effluent. An analysis of this method's operating costs in farms of 10,000, 20,000 and 50,000-head swine operation concluded that it would amount to an annual cost of between $13CAD to $9CAD per pig (Vallée et al., 1989; Gariépy et al., 1989; Cayer, 1989). This type of method is disadvantageously complex and costly.
Many methods are currently used in Europe comprising either removal of nitrogen or the recovery of nitrogen, phosphorus and potassium. They comprise drying and centrifugating the solid fraction and applying biological mechanisms of nitrification-denitrification to the liquid phase. The main methods and manufacturers are Agroclar™, Denitral™, OTV™. Technipompe™, Technolyse™, Val-Epurer™. For instance, the French method Agroclar is an aerobic biological method comprising a solid-liquid phase separation, aeration of the liquid phase and sludge concentration. It may remove up to 95% of the nitrogen and up to 70% of the phosphorus originally contained in the sludge. This process allegedly Costs about $10CAD/m3 when conducted in a centralized unit. These methods are not applicable to manure management in medium size farms because of their costs and complexity.
Kolber (2001) describes in U.S. Pat. No. 6,190,566 a method comprising a nitrification-denitrification treatment followed by a solid-liquid separation and a drying step of solids on drying beds. Teran et al. (2000) describes in U.S. Pat. No. 6,039,874 an aerobic method operated in lagoons after a first solid separation. Envirograin's Solution Biofertile™ first screens the manure and then treats the liquid portion aerobically and cold dries the separated solids in a centralized plant. This method would cost about 5 to $10CAD/m3 (FPPQ, 2001). CRIQ's Blosor Lisier™ method comprises decanting of the manure with concomitant sludges drawing, sand filtrating the supernatant, aerobic biofiltrating the filtered supernatant on an organic substrate (peat, compost, chips and barks), polishing the first biofilter's effluent oil mixed substrate and optionally, anaerobic digesting the decanted sludges. The Biosor Lisier™ method would cost about $10CAD to $15CAD/m3 (FPPQ, 2001).
Marr (1968) describes a method comprising biological aerobic thermophilic treatment ensured by microorganisms requiring a temperature of 55° C. This method ensures an increased oxidation of organic matter, a reduction in oxygen need and an increased stability of the system against chocks (Matsch and Drnevich, 1977). Under optimal conditions, two to three days of residence in the reactor are sufficient to oxidize organic matter (IAF, 1985; Bisaillon et al., 1984). Shooner and Samson (1996) describe a raw manure treatment performed in a reactor having thermophilic autothermal conditions. After strong aeration for a residence time varying between 5 to 15 days, a substantial reduction of COD, of BOD and of pathogenic microorganisms and an odors removal was achieved.
Anaerobic Treatment
Anaerobic treatment based methods seek to degrade organic matter in the absence of oxygen so as to promote gas (methane) formation which may then serve as an energy source for the farm. Bioscan's Biorek™ technology (FPPQ, 2001) and the German corporation Schwarting Umwelt Gmbh apply this method (Schwarting, 2002). McElvaney (2001) also described such a method in U.S. Pat. No. 6,254,775.
Composting
This solid phase fermentation process involves microorganism growth in a solid phase acting as substrate or support in the absence of water flow. Composting produces a significant release of heat and the temperature evolution follows three phases: a mesophilic phase (30–40° C.), a thermophilic phase with temperatures that may reach 70° C. and a cooling and maturation phase wherein the compost decreases to surrounding temperature. Temperatures of 60–65° C. are desirably maintained to achieve hygienization (i.e. microorganism destruction along with an active humidification without compost cooking (Mustin, 1987)). For manure composting, an optimal carbone/nitrogen ratio should be respected, namely between 25 and 35 (BNQ norms recommends a maximum of 25). Compost produces an odorless humus having a good fertilizing value: $1.11CAD/kg for nitrogen, $0.53CAD/kg for K2O, $0.95CAD/kg for P2O5. The volume reduction achieved by composting facilitates its exportation and spreading which would have been more difficult with raw manure (Texier, 1996; Ménart, 1996).
Texier (1996) describes composting methods performed in centralized units or on the farm. A starch based binding agent (Prolis™) is mixed with manure so as to increase its adhesion to straw. Composting at the farm with this method costs about $17CAD/m3. About 41% of this cost appears to be attributable to the starch based agent's cost. UQAR produced good results with maple and aspen chips and bark, whereas resinous residues were proved unsuccessful (Maheux et al., 1996). Composting according to the UQAR method coots about $12CAD/m3 for a large farm (11,000 m3 of manure annually). Giving out compost at the plant's door could decrease the cost to close to $8CAD/m3 and its sale would further reduce its cost. This approach is however limited by the lack of availability of maple or aspen residues in certain areas. Biomax's Compost Air™ technology, Meunerie J. B. Dionne and Fils' Eco-compost™ technology and Global Earth Products Inc.'s Marvel-Total™ Management System technology also use composting. The Eco-Compost™ and the Compost Air™ technologies allegedly cost about $5CAD to $10CAD/m3.
Filtration, Osmosis and Ultrafiltration Processes
Bilstad et al. (1992) describes a reverse osmosis process recovering 95% of nitrogen present in a liquid phase separated from manure. Tétrault and Grandbois (1999) in U.S. Pat. No. 5,885,461 describe a process used by Purin Pur™ comprising an ultrafiltration and two osmosis phases after a mechanical solid separation.
Drying and Fertilizer Production
Cloutier (1996) describes a method in which manure adsorbed on polymer pellets recovered from oil refineries is transformed in fertilizers and humus with equipment from Hydro-Québec and BN Métal. Legros (1998) describes a method of treating manure comprising drying it in a centralized plant. The fertilizer so produced would be rich in nitrates and phosphates, easy to transport, to spread and odorless. The application of this method by the Atrium corporation necessitates a 16 millions expenditure for the construction of a centralized plant.
Biological Treatments
A number of studies were performed on partial or complete microbiological treatment of pig manure. They teach means to eliminate manure odors at its root. Jolicoeur and Morin (1987) and Ralnville and Morin (1986) describe the use of Acinetobacter calcoaceticus spread on the piggery floor to degrade volatile fatty acids generating the odours (Bourque et al., 1987). Pabai et al. (1996) report that a number of studies seek to isolate microorganisms that produce lipase enzymes able to degrade there fatty acids. Other described treatments include lagooning along with algae (Chlorella) and cyanobacteria (Scenedesmus) production (de la Noüe et al., 1994); aerobic fixed bed along with aquatic plants (Salivinia molesta) (Yang and Chen, 1994); and stabilizing with strong aeration followed by cyanobacteria growth (Spirulina maxima) (Canizares and Domiguez, 1993). Methods for conferring commercial value to manure have been described including algae or aquatic plant (Phragmites sp) production (Cooper and Findlater, 1990), volatile fatty acid production by clostridium (Clostridium acetobutylicum, Clostridium butyricum) (Marx et al., 1990); 5-aminolevullnic acid herbicide production by Rhodobacter sphaeroides (Sasaki at al., 1990); production of biofertilizer having an antibiotic action with Streptomyces albidoglavus (Hayashida et al., 1988). Cooper and Findleter (1990) also describe the use of Phragmites sp to purify the liquid portion previously cleaned of its solid particles. This latter method is used for polishing effluents in more than 35 countries having tropical, semi-dry, hot-dry climates (Mandi et al., 1996), and Mediterranean, tempered and sub-polar climates (250 facilities in northern countries such as Denmark, Sweden, Finland and Norway). Such facilities have been used for 25 years in Germany and remain very efficient. This method works throughout the year including during the winter and MENVIQ described its effectiveness in treating wastewater (Bordeleau, 1993).
Flotation
Flotation has been used in a number of methods for treating wastewater. Jackson (1978) describes in U.S. Pat. No. 4,069,149 a wastewater treatment comprising separating solids from the bulk of the liquid by a gaseous flotation process, using the dissolved gas in the liquid as the source of gaseous bubbles for flotation purposes. Chudacek et al. (1997) describes in U.S. Pat. No. 5,660,718 a method for removing solid particles from liquids involving flotation with jet injecting air. Ramirez and Johnson (1980) describe in CA 1,091,830 and Coyne (1996) describe in U.S. Pat. No. 5,540,836 flotation methods involving external source of air. Itoh (1987) describes in U.S. Pat. No. 4,671,881 the use of pulverized coal and air to promote flotation. Roshenravan (1995) describes in U.S. Pat. No. 5,437,785 a method comprising an anaerobic digester, a free standing tank and a flotation cell. The gas produced during the anaerobic digestion is then compressed in the tank. The gas mixed with water is then directed from the tank to the flotation cell to assist the flotation. None of these references suggest using these methods to treat manure and they all use an added or compressed gas for their operation (methane, air or a mixture of air and other gases).
Few of the above-described methods are appropriate for use in medium size farms, namely the 2000-head swine operations. The treatment at the farm including disposal of the effluent in the environment presently requires important investments from the producers. Although it would finance a fraction of the method's installation and operation costs, the above methods do not include waste reclamation of the various products yielded.
There thus remains a need for a method of treating manure for medium size farms that avoid the drawbacks of the methods of the prior art.